Halecium secundum Jäderholm, 1904

Peña Cantero, Álvaro L., 2014, Revision of the Antarctic species of Halecium Oken, 1815 (Cnidaria, Hydrozoa, Haleciidae), Zootaxa 3790 (2), pp. 243-280 : 273-274

Halecium secundum Jäderholm, 1904

( Fig. 4 D–F)

Halecium secundum Jäderholm, 1904 : iii–iv; 1905: 11–12, pl. 4 figs 4–7; Redier, 1971: 70; Stepanjants, 1979: 109, pl. 16 fig. 8; Blanco, 1994a: 156; 1994b: 187; Vervoort & Watson, 2003: 86; Peña Cantero, 2004: 769; Peña Cantero et al., 2013: 747 fig. 6c.

Material examined. Syntype, SMNH Type-7948, Schwedischen Antarctic-Expedition 1901–1903, Stn 5, 64°20’S 56°38’W (SE of Seymour Island, Graham Region), four fragments up to 7 mm long.

Diagnosis. Polysiphonic, irregularly branched stems, up to 25 mm high. Branches originating either from abcauline side of hydrophore of primary hydrotheca or from inside hydrotheca. Usually, with ahydrothecate intermediate internode after apophysis. Hydrothecae alternately arranged in either one or two planes. Hydrotheca at the end of short, adnate hydrophore. Hydrotheca very slightly widening distally; rim not everted. Adcauline hydrothecal wall free or adnate to internode. Hydrothecal aperture slightly directed downwards. No secondary hydrothecae present. Male gonotheca elongated, cylindrical, distally with a wide, shallow furrow, and proximally with a sharp keel. Female gonotheca unknown. Cnidome consisting of microbasic mastigophores? and microbasic euryteles?

Description. Material studied consisting of four fragments up to 7 mm long; stems up to 25 mm according to Jäderholm (1904, 1905). Apparently, branching alternate. Longest fragment provided with four side-branches: first one originating from a primary hydrotheca through an apophysis and an intermediate, short, ahydrothecate internode before the first hydrothecate internode; the other three branches arising from the lateral of hydrophores. Seemingly, side-branches resting on large apophyses, frequently followed by an intermediate, short, ahydrothecate internode.

Stem and branches divided by alternately arranged nodes into relatively short and wide internodes ( Fig. 4 D–F). Hydrothecae alternately arranged, from more or less in one plane to about 90°.

Hydrothecae resting on adnate hydrophores ( Fig. 4 D–F); ratio between adcauline length of hydrophore and diameter at diaphragm c. 0.5. Hydrotheca low, very slightly widening distally ( Fig. 4 F). Adcauline hydrothecal wall usually adnate, sometimes free ( Fig. 4 F). Hydrothecal aperture perpendicular to long axis of internode or slightly directed downwards ( Fig. 4 D–F). Hydrotheca not surpassing distal node of internode. Coenosarc white.

Measurements (in µm). Hydrothecae: diameter at aperture 210–220, diameter at diaphragm 190–215, height 30–45. Internodes: length 525–600, diameter at distal part 180–230. Cnidome: microbasic euryteles? with rounded ends [range 11–12 x 6–6.5, mean 11.7±0.3 x 6.3±0.2 (n=10); ratio, range 1.7–2.0, mean 1.9±0.1 (n=10)] and microbasic mastigophores? with sharp ends (6.5–7.5 x 2–3).

Remarks. According to Jäderholm, the stem, c. 25 mm high, and the branches are stiff and polysiphonic (monosiphonic distally) and the branching is irregular in different planes. The female gonothecae are unknown, but there were male gonothecae, c. 1600 µm high and 320–360 µm wide, resting on very short pedicels. The gonotheca is elongated, cylindrical, weakly bent at distal part and provided with a wide, shallow furrow. It has a thin and high, very sharp keel in the proximal part.

Halecium brevithecum is similar to H. secundum in the low hydrothecae, the cnidome and the branching. The branches originate either just below the hydrotheca or from inside it in both species. Moreover, there is usually an ahydrothecate internode following the apophysis. Concerning the cnidome, the larger nematocysts are apparently of the same range. Finally, both species also have low hydrothecae, although they are slightly higher in H. secundum . In addition, the adcauline wall is distinctly more developed and completely adnate to the internode in H. brevithecum ( Fig. 4 A–C), whereas it is only slightly more developed and usually free in H. secundum ( Fig. 4 D–F). Furthermore, as shown above, H. brevithecum is also characterized by the reddish stems, the distinctly longer first hydrothecate internode of the branches, and the more or less perpendicular arrangement of the lower-order branches in relation to the previous ones.

Ecology and distribution. Halecium secundum has been found at depth between 40 (Peña Cantero et al. 2013) and 150 m ( Jäderholm 1904), on sponges and bryozoans ( Jäderholm 1904).

Halecium secundum seems to have a circum-Antarctic distribution, recorded from off Seymour Island, Graham region ( Jäderholm 1904), in West Antarctica, and from Tethys Bay, Ross Sea (Peña Cantero et al. 2013), in East Antarctica. However, it has also been reported in the Kerguélen area ( Redier 1971). If this record was confirmed, H. secundum would have an Antarctic-Kerguélen distribution.

Figures

FIGURE 4. Halecium brevithecum Watson, 2008. (A – C) internodes showing primary hydrothecae (A with basal ahydrothecate intermediate internode). Halecium secundum Jäderholm, 1904. (D – F) internodes showing primary hydrothecae. (All drawings from type material). Scale bar: 250 µm.